Psoriasis is an inflammatory skin condition characterized by exuberant overgrowth of the most superficial layer of skin cells, coupled with inflammation. Critical to the development of psoriasis is a type of blood cell called an activated T-lymphocyte. These cells, along with another type of blood-derived cell called the antigen-presenting cell, localize around the lesions of psoriasis. In fact, these two types of cells migrate into an area before overgrowth of skin cells begins. When effective treatments have been used for psoriasis, it has been demonstrated that the activated T-cells are depleted just before the skin lesions regress. This multi-center, randomized, multi-dose, dose-escalation study was developed by Dr. Krueger and collaborators at other universities to evaluate a synthetic protein that blocks the interaction between the antigen-presenting cell and the activated T-cell, and thus prevents proliferation of activated T-cells. Preliminary studies done by Dr. Krueger on the GCRC established that intravenous infusions of agents of this type were effective and well tolerated. The purpose of the current study was to determine if a new preparation generated using a slightly different method of production (a method which generated a product with enhanced stability) might be more effective than the previously used forms.